Heretofore, a corundum (the mineral name for aluminum oxide) has been widely used as a filler for filling in rubbers and plastics. For example, in silicone resin, silicone rubber and epoxy resin, the corundum is used as a heat-radiating filler. In the case of use as a high thermally conductive filler, the heat conducting performance is enhanced when the corundum is filled in a larger amount. However, if the amount filled exceeds 80 vol %, this causes a problem that the resin does not fit to the filler and cannot be shaped.
In order to solve this problem, a mixture of three alumina particle components differing in the particle size has been proposed (see, for example, JP-A-5-132576 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”(European Patent No.499585) and JP-A-2001-348488).
However, this corundum has a problem in that since three components differing in the particle size are merely mixed, fine particles are not successfully dispersed and also in that the corundum particle is inferior in the plane smoothness and therefore, has a large linseed oil absorption and the resin composition using this corundum has a high viscosity.
An object of the present invention is to solve the above-described problems and provide a corundum for filling in resins, which enables filling of the corundum in an ever-larger amount while reducing the viscosity by improving the blending ratio of a conventional corundum filled in resins such as plastic and rubber and ensures high thermal conductivity and high productivity. The object of the present invention includes providing a composition using the corundum.